broadband-modem-qmi: ensure we do not re-use old EPS registration state

When updating the registration state, in the case where LTE is not ready, ensure we reset the EPS registration state rather than leaving its old value. Else when the consolidated registration is built, it can wrongly think we are registered, e.g. the following case was happening: [modem0] consolidated registration state: cs 'home', ps 'home', eps 'home', 5gs 'unknown' --> 'home' a bit later [modem0] consolidated registration state: cs 'unknown', ps 'unknown', eps 'home', 5gs 'unknown' --> 'home' then it wrongly tries immediatly to connect and fails due to 'no-service'

On Qualcomm SC7180, running the following sequence would often reproduce it: mmcli -m 0 -d mmcli -m 0 --set-power-state-low sleep 10 mmcli -m 0 -e mmcli -m 0 --simple-connect="apn=broadband"